JP2959683B2 - Method for producing high-purity alumina fiber molded body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity alumina fiber molded article having high heat resistance and suitable as a high-temperature heat insulating material or a catalyst carrier.

[0002]

2. Description of the Related Art Alumina-based fibers are materials having high strength and excellent heat resistance, and are used in the form of flocculent or molded products. In particular, alumina-based fibers are prepared by using various binder components and matrix components. The molded article formed by molding has a small bulk density, is lightweight, and has a large heat insulating effect, and thus is suitable for a high-temperature heat insulating material or the like.

[0003] As a method of producing these alumina-based fiber compacts, conventionally, alumina, alumina-silica or alumina-silica-boron-based ceramic fibers are cut into appropriate lengths, which are then cut into silica fibers, alumina sol, or silica sol. For example, there is known a method in which an inorganic binder or an organic binder such as described above is added and molded and dried to produce (for example, JP-A-59-152281, JP-A-61-141683, and JP-A-64-42373). Gazettes). Furthermore, there is a method of firing the molded body produced by these methods at a more appropriate temperature for the purpose of improving heat resistance.

[0004] In short, the above-mentioned prior art uses a fiber after firing as a raw material in order to realize desired strength, heat resistance and the like, and contains a binder as an essential component to supplement the sinterability of the fiber. I have.

However, the alumina, alumina-silica or alumina-silica-boron-based ceramic fiber molded bodies produced by these methods have a problem in heat resistance such that cracks due to thermal shrinkage at high temperatures are liable to occur when used. When alumina fibers obtained by firing at a temperature of 1000 ° C. or higher are used, a high-purity alumina fiber molded body is obtained, but the sinterability of the fibers themselves is low. There is a problem that the sintering is insufficient, the strength of the molded body is reduced, and the fibers are easily crystallized at the time of use in a high temperature, and the fibers easily fall off from the surface of the molded body.

On the other hand, a method has been proposed in which a precursor fiber of alumina, silica, zirconia or the like is molded and fired to reduce energy consumption during production and obtain a fibrous refractory material having high strength (Japanese Patent Publication No. Hei 2 (1994)). -25873). However, in this method, it is difficult to maintain the fiber shape when the precursor fiber adheres at the time of storage and is dispersed and dispersed in a solvent, and is formed and molded.
There is a problem that cracks easily occur due to large shrinkage during firing.

[0007]

To summarize the problems of the prior art described above, when fibers fired at 1000 ° C. or higher are used as raw materials, sufficient heat resistance, strength, etc. are obtained unless alumina is of high purity. On the other hand, if it is not obtained, if it is highly purified, the sinterability will be insufficient and the strength will be reduced and the fiber will be peeled off from the surface of the molded product. Furthermore, energy consumption during production is large because fibers fired at 1000 ° C. or higher are used. When precursor fibers are used as a raw material, a molded article having high strength and excellent heat resistance can be obtained with low energy consumption, but the handling of the precursor fibers is not easy, and the precursor fibers adhere during storage. In some cases, a molded product cannot be obtained.

The present invention has been made in view of the above-mentioned state of the art, and has as its object to provide a method for stably producing a high-purity alumina fiber molded article having a light weight, high strength and excellent heat resistance by a simple process. . Such a molded article is extremely useful as a high-temperature insulating material, a base material of various composite materials, a catalyst carrier, or the like.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, formed and calcined calcined body fibers obtained in the process of producing high-purity alumina fibers to obtain high-purity alumina fibers. The present inventors have found that an alumina fiber molded product of the formula (1) can be obtained and completed the present invention. Although the precursor fiber is used, the calcined body can be used to maintain the fiber shape, which has the same effect as using the fiber as a raw material. In addition, since it is a precursor, there is no problem associated with the use of the fiber.

That is, the present invention provides a calcined body fiber obtained by spinning a spinning solution containing a high-purity alumina fiber precursor as a main component to form a precursor fiber, and calcining the precursor fiber at a low temperature. And then, if necessary, adding a binder component and / or a molding aid, and molding the resultant, and calcining the obtained calcined fiber molded article, thereby producing a high-purity alumina fiber molded article. Here, high purity means that 95% or more of alumina is contained based on the total amount of oxides in the fiber after firing. Therefore, components that do not constitute fibers are not included in the standards.For example, when a molded article is used as a functional composite material, it may contain catalytically active components other than fibers. Convert.

Hereinafter, the method of the present invention will be described in detail.

In the method of the present invention, first, a precursor fiber of high-purity alumina fiber is produced and calcined to obtain a calcined body fiber. “Precursor fiber” refers to a fiber obtained by spinning a spinning solution containing a high-purity alumina fiber precursor as a main component. The method for obtaining the precursor fiber is not particularly limited, and a method such as an inorganic salt method may be used. However, a slurry method for obtaining a high-purity precursor fiber (JP-B-57-27210, JP-A-63-27210) No. 75117).

Hereinafter, the method of the present invention will be described in detail based on the slurry method. First, the fiber after firing in an aqueous solvent solution such as an aqueous solution of a basic aluminum salt or a mixed solvent of water and a water-soluble solvent such as an alcohol, is based on the total amount of oxides in the fiber (hereinafter referred to as oxide basis). Powder of alumina having an average particle size of 0.1 μm or less corresponding to ４０40% by weight or an aluminum compound which becomes alumina by firing;
A slurry containing, by weight, a spinning aid and, if desired, 3% by weight or less of a sintering aid on an oxide basis is used as a spinning solution, which is spun and dried to obtain precursor fibers.

The basic aluminum salt used here includes basic aluminum chloride, basic aluminum nitrate, basic aluminum acetate, basic aluminum chloroacetate and the like. Also, improve the fluidity of the spinning raw material and reduce volatile matter during calcination and sintering,
As the powder to be added to improve the fiber strength, besides alumina, an aluminum compound which becomes alumina by sintering such as boehmite, bayerite, diaspore or coagulated boehmite can be used. Further, as a spinning aid for improving the spinnability of the spinning raw material, an organic compound such as ethylene glycol, glycerin, and acetic acid, or a water-soluble organic polymer compound such as polyvinyl alcohol, polyethylene oxide, and polypropylene oxide, or a mixture thereof is used. 0.1 to 10% by weight based on oxide
Added. Also, CuO, MgO, Zr as sintering aids
One or more oxides selected from O ₂ , PbO, Cr ₂ O ₃ , Fe ₂ O ₃ , MoO ₃ and TiO ₂ or these oxides by firing such as CuSO ₄ , MgCl ₂ , ZrCl ₂ Is preferred.

The precursor fiber thus obtained has a fiber diameter of about 5 to 200 μm, and has “high purity” on an oxide basis. Next, this is placed in an oxidizing atmosphere at 400
The calcined body fiber is calcined at a relatively low temperature of up to 1000 ° C. "Calcined body fiber" refers to a precursor fiber of 400 to 100.
The fiber is calcined at 0 ° C, and when dispersed in a solvent, the shape of the fiber is not damaged and there is no adhesion between fibers, but it is fired at a temperature of 1000 ° C or higher, which is higher than the calcining temperature. Refers to a fiber that has the property of being able to be sintered.
Usually, the manufacturing process of high-purity alumina fiber (precursor-calcination-
It is obtained before the final baking step in baking (1000 ° C. or higher). The calcining temperature is appropriately set within the above temperature range depending on the properties of the precursor fiber, the processing conditions in the molding step, the properties and mixing ratio of the molding aid or the binder component to be added, the properties of the target molded body, and the like. However, if the temperature is lower than 400 ° C., the fibers may be fused during the calcination treatment, and if the temperature exceeds 1000 ° C., the sintering of the fibers proceeds excessively, and the sintering activity of the calcined body fibers decreases. It is not preferable because the strength of the molded body cannot be obtained. Further, if a calcined product at 1000 ° C. or higher is used as a raw material of the molded body, dispersibility in a solvent such as water is poor at the time of molding (the calcined body fiber is easily dispersed). In this case, water cannot be used, and shrinkage during firing is large, so that dimensional adjustment is difficult, so that process control becomes difficult.

The calcined body fiber obtained in this manner is used in 0.1 g.
After adjusting to a length of 1 to 30 mm, it is molded to obtain a calcined body fiber molded body. The length may be set according to the intended use. The length of the calcined body fiber may be adjusted in the state of the calcined body fiber, but may be calcined after adjusting the length in the state of the precursor fiber. The calcined body fiber whose length has been adjusted in this way is dispersed in a solvent, and if necessary, a molding aid and a binder component are added.
Excess solvent is removed by a method such as evaporation, and if necessary, a means such as a pressure treatment is applied, followed by drying to obtain a molded body of calcined fiber. The molding aid and the binder component may be impregnated again after removing the excess solvent by papermaking, filtration and the like. In the present invention, since the calcined fiber has a sufficient sintering activity, the addition of a binder component, particularly an inorganic binder component, is not essential. This is in contrast to the prior art in which no molded article was obtained without the binder.

The shape of the calcined body fiber molded article is determined by removing the solvent in an appropriate mold, or cutting the molded article into a sheet, a board, a column, a tube, or a honeycomb. Any shape such as a shape can be used.

As the solvent to be used here, water is optimal because of its easy handling. However, depending on the type of the alumina fiber precursor to be used, dispersibility and volatility are taken into consideration, and methanol, ethanol, diethylene glycol and the like are used. Or an organic solvent such as an aromatic solvent such as benzene or toluene, a ketone solvent such as acetone or methyl ethyl ketone, or a mixed solvent thereof, or a mixed solvent of these organic solvents and water.

The molding aid optionally used in the molding step has the effect of improving the moldability and the physical properties of the molded article. For example, polyvinyl alcohol, polyvinyl methyl ether, polyacrylamide, polyethylene glycol, polyvinylpyrrolidone, glycerin, Examples include starch, cellulose acetate, methyl cellulose, carboxymethyl cellulose, alginic acid and the like. For the purpose of strengthening the sintering between fibers, a binder component in an amount of 10% or less on an oxide basis may be added. Preferred examples of the binder component include aluminum compounds such as aluminum chloride, aluminum phosphate, aluminum nitrate, aluminum sulfate, aluminum diacetate hydroxide, aluminum iodide, and ammonium aluminum sulfate. Here, when the alumina fiber precursor used in the production of the precursor fiber is used as the binder component, a homogeneous molded article having good affinity with the fiber can be obtained. Further, a gel forming agent such as agar, gelatin, or a metal alkoxide compound is added to the slurry of the calcined body fiber, and the mixture is treated under the gelling conditions of the respective gel forming agents to be gelled and solidified, and then dried. ,
By sintering, it is possible to obtain a molded body that is bonded while maintaining a state in which alumina fibers are randomly oriented in the solution.

By calcining the calcined body fiber compact thus obtained at a temperature of 1000 to 1900 ° C., which is higher than the calcining temperature, a high-purity alumina fiber compact can be obtained. . If it is lower than 1000 ° C., sintering is insufficient, and if it is higher than 1900 ° C., a problem may occur in maintaining the shape of the compact. The firing time is appropriately set according to the size and shape of the molded body. In addition, when the organic component remains in the calcined body fiber molded body, if the heating rate during firing is too fast, the decomposition and combustion of the organic component occur rapidly, and the molded body is cracked, Sintering between the fibers becomes difficult to progress,
Since there is a possibility that the strength of the molded body may be reduced, the heating rate during firing is preferably 200 ° C./hr or less.
From room temperature to 1250 ° C. where decomposition and desorption of organic components, change in composition of binder components and initial sintering proceed, 5
It is preferable that the heating rate is 0 ° C./hr or less.

Since the high-purity alumina fiber molded article obtained by the method of the present invention is molded and calcined at the stage of the calcined fiber, the adhesion between the fibers is strong and has a compressive strength of 5 to 80 kg / cm ^2. Has a bulk density of 0.05 to 1.0 g /
cm ³ and a lightweight, porosity fine pores are uniformly distributed 7
It is a porous material of 5 to 98%, has high heat resistance up to about 1900 ° C., and is a material suitable for applications such as a high-temperature insulating material and a catalyst carrier used under high-temperature conditions. In addition, a product molded using a gel forming agent is characterized in that it has mechanical, thermal, and electrical isotropic properties without fiber orientation. Furthermore, the high-purity alumina fiber molded body can be cut into an arbitrary shape, and contains a substance that emits infrared light of a specific wavelength on its surface, or has a specific color tone such as black. It can be used by applying a Yu medicine to enhance the heat insulation effect and the heat reflection efficiency. By using a functional additive such as a catalytically active component in advance, it can be used as a base material for various functional composite materials.

[0022]

EXAMPLES The method of the present invention will be described more specifically with reference to the following examples.

Example 1 4.2 parts by weight of aluminum chloride, 46.7 parts by weight of anhydrous basic aluminum chloride, 10.2 parts by weight of γ-alumina fine powder having an average particle size of 0.02 μm, and 0.1 part of magnesium chloride.
43 parts by weight are dissolved and dispersed in 34 parts by weight of water, and polyethylene oxide (average molecular weight: about 1,000,000) is added to the slurry.
4.5 parts by weight were added and mixed well to obtain a spinning dope. This stock solution was spun to obtain a precursor fiber having a fiber diameter of 20 μm.
This precursor fiber was passed through an electric furnace having a maximum temperature of 900 ° C. for a residence time of 1 minute to obtain a calcined body fiber. 400 g of the calcined body fiber cut to a length of 1.0 mm was added to water 2
After dispersing in 0 liter, filtration and papermaking were performed. After the papermaking, 1 liter of a 1% aqueous solution of polyvinyl alcohol was impregnated as a molding aid and molded, and dried at 105 ° C. for 24 hours to obtain a calcined body fiber molded body of 250 × 250 × 20 mm. The calcined body fiber molded body is heated to 1100 ° C. at a heating rate of 100 ° C./hr, then to 1450 ° C. at a heating rate of 50 ° C./hr, and heated at the same temperature for 4 hours. , And sintered. The obtained molded body has an alumina purity of 9
9.5% α-alumina, with compressive strength of 15kg / c
m ² , a bulk density of 0.40 g / cm ³ , and a porosity of 89%. (Example 2) The same precursor fiber as prepared in Example 1 was 1.5 m in length.
Then, 545 g cut into a piece of m was put in an electric furnace and kept at a maximum temperature of 500 ° C. for 1 hour to obtain a calcined body fiber. This calcined body fiber was formed in the same manner as in Example 1, and 250 × 250
A calcined body fiber molded article of × 35 mm was obtained. This calcined body fiber molded body is heated to 1000 ° C. at a rate of 100 ° C./hr, then to 1200 ° C. at a rate of 50 ° C./hr, and further to 100 ° C./hr. At 1700 ° C
Then, the mixture was heated at the same temperature for 4 hours and sintered. The obtained molded article was an α-alumina substance having an alumina purity of 99.5%, a compressive strength of 10 kg / cm ² , a bulk density of 0.28 g / cm ³ , and a porosity of 92%.

Example 3 600 g of a calcined body fiber having a length of 1.0 mm obtained in the same manner as in Example 1 except that the calcination temperature was 800 ° C., was filtered in the same manner as in Example 1. , Paper-made. After the papermaking, a slurry obtained by dispersing 150 g of the same spinning solution as used in Example 1 in 1.5 liters of water, also serving as a molding aid and a binder component, was impregnated, dried at 105 ° C. for 24 hours, and dried at 250 ° C. for 250 hours.
A calcined body fiber compact of × 250 × 35 mm was obtained. The calcined body fiber molded body was heated at a heating rate of 100 ° C./hr for 110
The temperature was raised to 0 ° C, and then 14 ° C at a rate of 50 ° C / hr.
The temperature was raised to 50 ° C., heated at the same temperature for 4 hours, and sintered. The obtained molded article was an α-alumina substance having an alumina purity of 99.5%, a compressive strength of 20 kg / cm ² , a bulk density of 0.35 g / cm ³ , and a porosity of 90%. (Example 4) 250 x 250 x 20 m obtained in the same manner as in Example 3
m at a heating rate of 50 ° C./hr.
The temperature was raised to 000 ° C., then to 1450 ° C. at a rate of 25 ° C./hr, heated at the same temperature for 4 hours, and sintered. The obtained molded body was an α-alumina material having an alumina purity of 99.5%, a compressive strength of 50 kg / cm ² , a bulk density of 0.60 g / cm ³ , and a porosity of 83%.

[0025]

According to the method of the present invention, the alumina fiber is molded in the state of the calcined body fiber and then fired, so that
Compared with the conventional method of mixing and molding alumina fibers fired at 0 ° C or higher with a binder component, the sintering activity between the fibers is higher, and an inorganic binder is added if there is no special need for adjusting density and strength. Thus, it is possible to obtain a high-purity alumina fibrous formed body having strength enough to withstand use. In the method of the present invention, the step of sintering the fiber at 1000 ° C. or higher can be omitted, and the calcined body fiber has better dispersibility in the solvent at the time of molding as compared to the fiber fired at 1000 ° C. or higher. Compared to the method using a precursor fiber, there are advantages such as a small shrinkage at the time of firing and easy dimensional adjustment, and the process can be significantly simplified. 1000 ° C
When using the fiber fired above, it must be fired at a temperature higher than the firing temperature of the fiber, but since it can be sintered from a relatively low temperature, by setting the firing method appropriately, The degree of crystallization of alumina in the molded body can be adjusted accordingly. On the other hand, the calcined body fiber has better preservability compared to the precursor fiber in the conventional method, has high flexibility and is easy to handle at the time of molding, and also has a shrinkage during firing of the obtained calcined body fiber molded body. Since the ratio is small and the shape retention is good, it is possible to obtain a molded article having a larger or more complex shape than when the precursor fiber is used.

The alumina fiber molded article obtained by the method of the present invention is a porous material having high strength, high heat resistance, and in particular, is less likely to generate and expand cracks caused by a heat cycle. It is suitable as a high-temperature refractory heat-insulating material and a catalyst carrier to be used at high temperatures.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Takashi Shinbo 1, Kokufucho, Tochigi City, Tochigi Pref. Mitsui Mining Co., Ltd. Central Research Institute (72) Inventor Hiroshi Nakamura 2-1-1, Nihonbashi Muromachi, Chuo-ku, Tokyo Mitsui (56) References JP-A-63-75117 (JP, A) JP-A-2-25873 (JP, A) JP-A-2-307953 (JP, A) (58) Fields studied (Int .Cl. ⁶ , DB name) C04B 38/00-38/10 D01F 9/08-9/22

Claims (3)

(57) [Claims] A spinning solution containing a high-purity alumina fiber precursor as a main component is spun into a precursor fiber, and a calcined body fiber obtained by calcining the precursor fiber is optionally used with a molding aid. A method for producing a high-purity alumina fiber molded body, comprising molding and calcining the obtained calcined body fiber molded body. 2. A spinning solution containing a high-purity alumina fiber precursor as a main component is spun into a precursor fiber, and a calcined body fiber obtained by calcining the precursor fiber is added with a binder component. A method for producing a high-purity alumina fiber molded body, comprising molding by using an auxiliary agent and calcining the obtained calcined body fiber molded body. 3. A spinning solution containing a high-purity alumina fiber precursor as a main component is prepared by adding a powder of alumina or an aluminum compound which becomes alumina when calcined to a solution prepared by dissolving a basic aluminum salt in water or an aqueous solvent; The method for producing a high-purity alumina fiber molded body according to claim 1 or 2, wherein the slurry is a slurry obtained by adding a sintering aid, if necessary.